This disclosure relates to the manufacture and testing of semiconductor wafers, and in particular to a defect card for individual semiconductor dies.
Generally, as industrial products become more complex, their quality must also increase. This is particularly true for semiconductors, where functional or parameter tests are typically performed at various stages during their manufacture.
Semiconductive dies are typically manufactured on wafers (e.g., silicon). Each wafer is cut into a plurality of dies. The size of the individual die and the number of die per wafer are determined by design and the technology.
The dies are tested for their functional capability during a post semiconductor manufacturing procedure referred to as probing. Probing is typically performed before the semiconductor wafer is cut into discrete die, in a measuring apparatus referred to as a prober. In the prober, defective dies are marked with ink, or x-y location data indicative of their position on the wafer is stored in memory. A ratio of the functioning dies (i.e., the unmarked dies) to the total number of the manufactured dies is a factor in determining the cost-effectiveness of the semiconductor manufacturing process.
Due in part to complex die manufacturing methods, systematic flaws typically occur in limited areas of the wafer, while random or stochastic flaws can be distributed over the entire semiconductor wafer. Statistical methods may be applied to detect substantially all the defective dies on the wafer, which includes those defective dies having a latent flaw that can increase the probability of a later breakdown of the die.
In a typical semiconductor wafer, dies are arranged in rows and columns, such that, except proximate edges of the wafer, each die is surrounded by eight adjacent dies. Therefore, if defective dies are clustered in one area of the wafer, there is a higher probability that dies adjacent to those defective dies are also flawed since clustered flaws indicate a systematic flaw. This premise is implemented in a method known as the x/8 rule, where x dies surrounding a defective die are recognized as flawed, and the remaining (8−x) dies are marked as flawed, for example, by inking For example, the ⅜ rule states that in the event three defective dies surround one defective die, the remaining 5 dies that surround this defective die should also marked as defective. This procedure may be repeated multiple times, where the dies inked later are assumed to be defective in this iteration.
One disadvantage of such a method is that edges of contiguous regions are not recognized. Another disadvantage is that sufficiently high defect densities that are statistically distributed over the wafer result in the marking of all dies located in this entire region as defective. Examples of this are shown in FIGS. 2 and 4, where dies recognized as defective are marked as “defective”, and dies surrounding the defective dies are marked as “inked”. Specifically, FIG. 2 illustrates a wafer having a uniformly distributed defect density of 3.0/cm2. Notably, nearly the entire region of the wafer is inked using the described ⅜ rule. FIG. 4 illustrates a circled region “I”, in which the edges of contiguous regions are not recognized during the probing and, therefore, are inked as defective.
There is a need for an improved method of creating a defect card, which avoids the above-mentioned disadvantages, and a prober for performing this method.